All the installations that are required for producing rolled products may be combined in a rolling mill. Depending on the type of forming, a distinction is drawn between hot and cold rolling mills. In the hot rolling mills or wide hot strip rolling mills, roughed slabs or ingots, usually called slabs for short, are processed into hot strip. This hot forming is one of the processes that follow the primary forming (ingot casting, continuous casting). In this process, the rolling stock is heated to temperatures of up to 1350° C. and, preferably while above its recrystallization temperature, is reduced to a predetermined thickness by pressure in a roll nip of the rolling mill. The overall complex of a hot rolling mill may include: raw material stores; heating furnaces, descaling installations; roughing and finishing trains with different numbers of stands, groups of stands and types of stands; coilboxes; cooling devices; adjusting devices; coiler(s) and finished material stores. Furthermore, a rolling mill may include stores; transporting and guiding devices and extensive regulating, controlling and measuring systems.
Since the finished product (usually steel or aluminum strip) can only rarely be rolled out in a single pass, a number of roll stands are combined to form a rolling train, in which a number of rolling passes are performed in accordance with the number of passes through the stands. In hot rolling mills, a distinction is drawn between the roughing train and the finishing train, the slab being preprocessed in the roughing train in order subsequently to be rolled out to its final dimensions in the finishing train, usually comprising five, six or seven stands.
In the rolling mill, the roll stands represent the central installation parts. The roll housings of the roll stands must absorb the high rolling forces that occur and thereby expand as little as possible. The roll bearings of the roll housings provide correct guidance of the rolls and transfer the rolling forces to the roll housings via the adjusting system, the adjusting devices of the adjusting system serving for horizontal and vertical positioning of the rolls. The adjusting devices may be actuated mechanically, electromechanically or hydraulically. Generally, during the rolling of wide hot strip, four-roll stands, known as four-high stands, are used, comprising two working rolls and two backing rolls, the backing rolls usually having a greater diameter than the working rolls.
One of the problems when rolling slabs or the strips produced from them is that the rolling stock to be rolled in a roughing train has a variation in thickness over its width. The aim is generally to use rolling as a means of producing strips which on the one hand have a thickness over the width that is substantially symmetrical in relation to the middle of the strip, i.e. have no taper, and on the other hand have as little curvature as possible over the length of the rolling stock, i.e. have no camber.
However, this is difficult to achieve whenever a rolling stock that is already formed with thickness taper during the first rolling within the hot rolling train has to be rolled. The thickness taper of the rolling stock is generally a result of the casting process and the subsequent cooling and further processing, in particular halving, of the cast slabs.
If rolling stock with a thickness taper is to be rolled out into a slab with a substantially rectangular cross section, then there is generally a stronger material flow, particularly longitudinal flow, on the “thick” side of the slab than on the “thin” side of the slab on account of the volume being maintained. A result of this differing material flow in the longitudinal direction of the rolling stock is the formation of a camber. A cambered rolling stock may, depending on the degree of camber, lead to difficulties in the subsequent processing of the rolling stock. The formation of the camber may be so pronounced that further processing of the rolling stock is impossible.
Laid-out patent application WO 2006/119984 A1 discloses a method and a device for specifically influencing the geometry of a near-net strip in a roughing stand, with slabs being rolled out into near-net strips in one or more roughing stands. A method which makes it possible to produce straight near-net strips without thickness taper and without lateral curvature can be provided by achieving specific influencing of the roughing strip geometry on at least one roughing stand by corresponding regulating means of a dynamic adjustment in the roughing stand being interconnected with fast and powerful lateral guides upstream and downstream of the roughing stand in such a way that a slab with camber and thickness taper is transformed specifically into a straight near-net strip with no taper in one or more passes in a reversing or continuous operating mode.
A disadvantage of the teaching specified in the above laid-open application is that only straight near-net strips without thickness taper and without lateral curvature are produced there. This form of the rolling stock with no camber and with no taper may, however, be lost again by subsequent processing of the rolling stock. Furthermore, use of the fast and powerful lateral guide may entail the occurrence of high forces, which may lead to defective lateral guidance and great, and therefore disadvantageous, loading of the edge of the near-net strip.